It is well known in the art of subsurface oil production that solution gas is also often produced to surface. Such gas commonly travels to surface in the well casing (thus called “casing gas”). Casing gas has traditionally been vented to the atmosphere or flared, rather than conserved through onsite storage or pipelining to remote locations generally due to cost considerations when addressing relatively low volumes of casing gas.
Government regulations are increasingly reducing vent gas allowances, thus requiring increased flaring or conservation of the casing gas. However, flaring introduces increased risk, landowner concerns, and possibly area class spacing issues. In addition, gas conservation may not be possible or economical in certain situations. Gas conservation may also be problematic where the casing gas is sour—increasing costs associated with necessary controls—or where the gas is of low grade or does not meet gas system specifications.
In some prior art systems, the oil pumps are driven by engines that are configured to burn natural gas, and specifically natural gas produced from the well. This provides an option for addressing concerns around venting or flaring of casing gas. For example, U.S. Pat. No. 9,394,770 to Boot et al. teaches using produced gas at a remote location to power an onsite engine, and using the engine to power a generator to produce electricity for the well location. In a further example, United States Patent Application Publication No. 2010/0038907 to Hunt et al. teaches capturing casing gas to drive the pump engine, and also using the engine to drive one or more generators to create electricity.
However, it is known that gas volumes are not static during production, and volumes can vary substantially over time. Allowing an engine to burn whatever volume of gas is produced can thus result in the engine operation increasing to dangerous levels, possibly to redline where damage to the engine can occur. Well sites are commonly in remote locations, and therefore it is likely that such dangerous engine conditions would occur when personnel are not at site to address the issue, and engine failure could lead to pump shutdown and production losses. Complex equipment solutions may be possible, but they could be economically unfeasible, and as indicated above storage or pipelining of excess gas may also be undesirable or unavailable.
What is needed, therefore, is a means to reduce casing gas venting and flaring while reducing undesirably expensive equipment line-ups and gas storage or pipelining.